This invention concerns a continuous casting contrivance along with a process for its production.
Conventional cooling forms for continuous castings require molds that are costly, compression molded and consisting of electrographite, and become ever more expensive as a function of the continually rising costs for energy, since each mold must be newly produced as a precision rotating part for each casting.
The graphite molds used for the continuous casting processes employed today project upwardly into the heat retaining crucible or oven, with their cooling parts contained in a metal cooler. Up until the present time, molds almost exclusively have been graphite, since this material is the only one possessing the characteristics desirable and required for continuous casting processes. Such characteristics include non-wettability and non-solubility of the graphite through the metal to be cast, durability of the form at the casting temperature, relatively good heat conductance, and self-lubricating and parting characteristics, respectively.
However, graphite molds also have a disadvantage. The graphite material is not resistant to oxidation in the range above 550.degree. C., frequently has defects, flaws, cracks, etc., and is very sensitive to frictional stress by the hard casting shell. This results in formation of grooves that impair the surface quality of the castings during continuous casting. Furthermore, graphite molds are very sensitive to impact, bending and tensional stressing.
The casting capacity of a graphite mold is dependent on the sizes occassioned by the material properties, and the heat flow through the wall of the mold. In order to raise the casting capacity one often uses as small a mold wall thickness as possible. However, large and thin-walled hollow cylindrical molds become very friable (brittle) and are then not safe. Even small transverse forces or a hard touchdown of the mold can lead to cracks or ruptures often not noticed prior to casting, and prone to cause serious and dangerous accidents, namely breakthroughs or so-called runouts.
A further serious disadvantage of the mold consisting of graphite is, in addition to the high costs for materials, the fact that much expert knowledge, care and time are required in the production of a graphite mold. Further needs are expensive tools, special suction-removal means, etc. Each mold must be precisely fitted, ground in or pressed into the metal cooler surrounding it in order to guarantee an adequate heat transfer. Very seldom is one adapter the same as another and often it is also precisely the large, thin-walled molds that break when knocked out of the metal cooler, because of the required, high degree of frictional adherence.
Additionally, problems frequently occur in production with material defects. One defect is warping of the cooler surrounding the graphite mold, even though used only a relatively short period of time. The cooler bulges out from uncontrolled heat stressing, to form an air gap between the mold outer wall and cooler that strongly reduces the cooling capacity and, therewith, casting capacity.
Finally, mold wear is a principal factor in production costs. On the average, the proportional costs for mold costs presently lie at 0.10 German Marks per kg of generated casting.
Disclosed in DE-OS 20 58 51 and DE-GM 18 54 884, is a mold that is split, in the longitudinal direction, into two or three parts, the overall structural length of the mold being relatively great because of the different casting conditions. In the first mold section, only slight heat need be removed below the floor of the melt crucible. A greater proportion of heat must be removed in the adjoining section. These types of molds have not proven effective and, when not using graphite, yield defective casting results.